Method to chase weld lines by timing and positioning of gates

ABSTRACT

An apparatus and method for eliminating mold lines when molding a part having ferromagnetic pigments is provided. A mold assembly having a mold with a cavity and valve gates is formed. Pucks are fitted at the gates to collect residual cold plastic. The calculation of a specific sequence and timing of the opening of the valve gates is determined based on a calculation of the total number of valve gates needed to fill a part while maintaining acceptable injection molding pressure. Once calculated, the gates are positioned around the mold cavity to balance flow length ratio. A primary gate is chosen for initial injection. The time for the material to flow from the first to the second gate is established. The second gate is opened after the flow front reaches the second gate. This pattern continues until all valve gates are opened.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2015/056374, filed on Oct. 20, 2015. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to injection molding methods of materialhaving a molded-in metallic pigment. More particularly, the presentdisclosure relates to a method for the injection molding of materialhaving dispersed metallic pigment when forming a molded-in metallicpart.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Popular color trends in consumer products include various metallic orpolychromatic paint colors. The appearance of stainless steel in kitchenappliances and metallic surfaces on electronic products are very popularamong consumers. Enthusiasm for metallic paint extends to exterior paintschemes for automotive vehicles. This type of paint is often preferredby vehicle buyers as it highlights the contours and bodywork of thevehicle more than solid paint. Metallic paint also renders the paint asparkling effect, thus adding to the overall attractiveness of thevehicle.

As an extension of exterior metallic paint, vehicle purchasers alsofrequently prefer metallic decorative parts in the automotive interior.Some of these interior components are made out of actual metal. However,many of them are made out of other materials such as plastic and arethen decorated to appear to be metal.

One way to decorate plastic is to overcoat the substrate using a paintor a film, but this approach can be relatively expensive and is prone toimperfections. In order to reduce manufacturing cost, many companies areworking on perfecting injection molding methods using metallic pigmentin the resins in an effort to eliminate the painting process.

While the theory has merit, in practice manufacturers have found thatwhen using metallic pigment in resins, the orientation of the metallicpigment in the resin cannot be controlled. As a result, the metallicpigment sometimes shows up as flow marks or dark spots on the A-surface.In addition, when the part being molded is relatively thick, metallicpigment is often wasted since the pigment is only needed on theA-surface.

An additional challenge faced by manufacturers when forming molded-inmetallic parts relates to operation of the mold cavity during theinjection molding process. During the molding process, molten plasticenters a mold through a sprue and goes through series of runners. Moltenplastic then enters the tool cavity through gates. When there aremultiple gates to form a part, flow fronts meet and form weld linesduring the molding process. Visible weld lines are considered as surfacedefects and not acceptable for class-A surface parts. Minimizing weldlines is important since a part is weaker at the weld line.

Accordingly, an efficient and economical method to mold vehicle interiorcomponents using a metallic pigment in the resin that avoids flow marks,dark spots or weld lines while minimizing wastage is a desirable goalfor automotive manufacturers.

SUMMARY

The present disclosure provides a method and apparatus for forming partshaving metallic pigments. According to the present disclosure, asequential valve gate system having a specific timing gate openingsequence is used to inhibit weld lines.

Initially, a mold assembly having a mold with a cavity and an array ofgates is formed. At each gate, a large puck is fitted to collect anycold plastic that may remain after the previous shot. Once the moldassembly is formed, the calculation of gate opening and positioning isundertaken.

To make the calculations of gate opening and gate positioning, thespecific sequential valve gate operating system and timing gate openingsequence is based initially on a calculation of the total number ofgates needed to fill a part while maintaining acceptable, or apredetermined, injection molding pressure. Once this initial calculationis made, the gates are positioned around a mold cavity to balance flowlength ratio. The primary gate is then chosen. After this selection, theflowing material is injected and the timing for the flow from the firstgate to the second gate is established. The second gate is then openedimmediately after the flow front passes the third gate. This patterncontinues until all of the gates are opened.

According to the method of the present disclosure, where a part withouta hole or an opening is being formed, weld lines can be positioned orinhibited by proper gate location and sequencing gate opening.

The above advantages and other advantages and features will be readilyapparent from the following detailed description of the presentdisclosure when taken in connection with the accompanying drawings.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a back view of a mold part produced by a method according tothe present disclosure;

FIG. 2 is an illustration of a mold apparatus having the molded part ofFIG. 1 shown therein in association with a series of valve gates; and

FIG. 3 is an illustration of a portion of the mold apparatus of FIG. 2illustrating a valve gate in relation to a puck, mold passageways, and amold cavity.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In the following figures, the same reference numerals will be used torefer to the same components. In the following description, variousoperating parameters and components are described for differentconstructed forms. These specific parameters and components are includedas examples and are not meant to be limiting.

In general, the method and apparatus for providing a way of inhibitingweld lines in a molded-in metallic product having metallic pigment inthe resin is discussed hereinafter. The disclosed method and apparatusenable the practical production of a molded-in metal part without weldlines by calculating gate opening times and gate positions when formingthe mold. By opening properly positioned gates at certain times duringthe mold process, undesirable weld lines are reduced and an excellentA-surface results.

More particularly, the present disclosure overcomes the challenges facedby prior art approaches of molding parts with metallic pigment in theresin. Particularly, the present disclosure provides for the use offerromagnetic pigment in resins and magnetic field adjacent the mold inthe injection molding tool to thereby reduce the use of metallic pigmentand, as a result, reduce manufacturing cost while providing an excellentA-surface that is substantially free of flow marks and dark spots.

Referring to FIG. 1, a molded-in metallic part 10 produced according tothe disclosed method is illustrated. The molded-in metallic part 10 isillustrated for example only, as a wide variety of parts may be producedaccording to the disclosed method using the illustrated apparatus. Thusthe molded-in metallic part 10 is only shown for illustrative purposesand is not intended as being limiting.

The molded-in metallic part 10 shown in FIG. 1 includes a part body 12.The part body 12 includes a first arm 14 and a second arm 16. The firstarm 14 and the second arm 16 are connected by an intermediate arm 18. Anarray of attachment clips 20 are formed in the first arm 14, the secondarm 16 and the intermediate arm 18. The attachment clips 20 arestrategically located on the part body 12 so as to proper align withfastener holes formed in the substrate (not shown) to which themolded-in metallic part 10 is fitted.

To improve the appearance of the A-surface of the molded-in metallicpart 10, the present disclosure further includes a sequential valve gatesystem and timing opening sequence that can position or inhibit moldlines. This arrangement is illustrated in FIGS. 2 and 3.

Referring to FIG. 2, a mold apparatus 30 is shown. The molded-inmetallic part 10 is shown within the mold apparatus 30. To form themolded-in metallic part 10, a sequential valve gate system and timinggate opening sequence is applied, thereby positioning or inhibiting weldlines. A series of valve gates is provided that includes a first valvegate 32, a second valve gate 34, a third valve gate 36, a fourth valvegate 38, a fifth valve gate 40 and a sixth valve gate 42. A greater orlesser number of valve gates are possible. Calculation of the totalnumber of valve gates is based on the number required to fill a partwhile maintaining acceptable, or a predetermined, injection moldingpressure. Placement of each valve gates around the mold cavity is madeso as to balance the flow length ratio. Arrows indicate the direction ofmaterial flow.

The positions of the first valve gate 32, the second valve gate 34, thethird valve gate 36, the fourth valve gate 38, the fifth valve gate 40,and the sixth gate 42 are based on the calculated balance flow lengthratio. The timing of the opening and closing of the gates is based onthe material used and the flow rate from the time the material leavesthe first valve gate 32 to the time the flowing material takes to passthe second valve gate 34, and so on, until the flow completely fills themold cavity. The first valve gate 32, the second valve gate 34, thethird valve gate 36, the fourth valve gate 38, the fifth valve gate 40,and the sixth gate 42 are attached to a controller 44. The controller 44is programmed to regulate the sequence of gate opening and the timing ofthe gate opening and closing.

After deciding on a primary gate, in this instance the first valve gate32, a determination is made as to how much time is required for theinjected material flow to leave the first valve gate 32 before reachingthe second valve gate 34. The second valve gate 34 should be openedimmediately after the flow front passes the second valve gate 34. Thethird valve gate 36 is opened immediately after the flow front passesthe third valve gate 36. This pattern continues until all valve gates32, 34, 36, 38, 40 and 42 are opened. When producing a part without ahole or an opening, weld lines can be positioned or inhibited or eveneliminated by proper valve gate location and sequencing the opening ofthe gates.

The present disclosure provides an additional feature to inhibit surfacedefects at each of the valve gates. This arrangement is illustrated inFIG. 3 in which a portion of the mold apparatus 30 is shown. The firstvalve gate 32 is also illustrated, although it is to be understood thatthe arrangement described herein relative to the first valve gate 32 canapply to any or all of the above-described valve gates.

The first valve gate 32 includes an inlet 50 and an outlet 52. Theoutlet 52 is fluidly associated with a flow passageway 54 and a puck 56.A mold cavity 58 is formed within the mold apparatus 30 to form themolded part 10. The puck 56 collects the cold plastic remaining from theprevious injection shot, thus inhibiting surface defects formed at eachgate.

In use, a mold is formed having a part cavity and an electromagnetplaced in a location adjacent the part cavity. A quantity of resin isplaced in the part cavity, together with a quantity of ferromagneticpigment. The electromagnet is energized, causing the ferromagneticpigment to move in the direction of the electromagnetic, thus forming anarea of concentrated pigment. This concentrated area is the A-surfaceonce the part is cured. In addition, by forming the part using asequential valve gate system and timing gate opening sequence, thepositioning or elimination of weld lines is possible. The result is apart substantially free of flow marks, dark spots and weld lines on theA-surface.

The above-described logic is only exemplary and it is to be understoodthat many variations may be made without deviating from the presentdisclosure as disclosed and described. For example, mold may have morethan one mold cavities formed therein for the simultaneous molding ofmolded-in metallic parts.

One skilled in the art will readily recognize from such discussion, andfrom the accompanying drawings and claims that various changes,modifications and variations can be made therein without departing fromthe true spirit and fair scope of the present disclosure as defined bythe following claims.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

What is claimed is:
 1. A method for molding a part comprising: calculating a number of valve gates for a mold cavity; calculating a position of each valve gate around the mold cavity to balance a flow length ratio; forming a mold with the mold cavity, wherein the mold comprises a plurality of valve gates equal to the calculated number of valve gates and each of the plurality of valve gates is located at the calculated position of each valve gate around the mold cavity; injecting material into a first valve gate of the plurality of valve gates; determining a time for the material to travel from said first valve gate to a second valve gate of the plurality of valve gates; and opening said second valve gate after a flow front of the material passes said second valve gate, wherein the plurality of valve gates are controlled to maintain a predetermined injection molding pressure in the mold cavity.
 2. The method for molding a part of claim 1, wherein a material-collecting puck is attached to each of the plurality of valve gates to collect any cold plastic that may remain after a previous injection of material.
 3. The method for molding a part of claim 1 further comprising including basing gate timings on a length of time for the material to flow from said first valve gate pass said second valve gate.
 4. The method for molding a part of claim 1 further comprising a step of identifying said first valve gate.
 5. The method for molding a part of claim 1, wherein said material is metallic.
 6. The method for molding a part of claim 1 further comprising attaching a controller to said plurality of valve gates.
 7. The method for molding a part of claim 6 further comprising a step of programming said controller to control a time of opening of each of said plurality of valve gates based on a flow rate to inhibit weld lines in the part.
 8. A method for molding a part comprising: calculating a number of valve gates in a mold to fill a part cavity while maintaining a selected molding pressure, wherein the calculated number of valve gates comprises a first valve gate and a second valve gate; forming a mold having the part cavity with the calculated number of valve gates, wherein each valve gate is positioned around the part cavity to balance a flow length ratio; and inserting flowing material through said valve gates to form a molded-in metallic part using a specific sequence of gate openings according to a selected gate timing, wherein the inserting flowing material through said valve gates comprises injecting material into a first valve gate, determining a time for the material to travel from said first valve gate to a second valve gate, and opening said second valve gate after a flow front of the material passes said second valve gate, wherein the calculated number of valve gates are controlled to maintain the selected molding pressure in the part cavity.
 9. The method for molding a part of claim 8 further comprising attaching a material-collecting puck to each valve gate.
 10. The method for molding a part of claim 8, wherein the specific sequence of gate openings according to the selected gate timing for the valve gates is based on determining a length of time for the flowing material to reach a downstream valve gate after leaving an upstream valve gate.
 11. The method for molding a part of claim 8 further comprising the step of determining a primary valve gate.
 12. The method for molding a part of claim 8, wherein said material is a molded-in metallic material.
 13. The method for molding a part of claim 8 further comprising attaching a controller to each valve gate.
 14. The method for molding a part of claim 13 further comprising programming said controller to control an opening time of said valve gates based on a selected flow rate.
 15. The method for molding a part of claim 1, wherein the plurality of valve gates are controlled to maintain the predetermined injection molding pressure in the mold cavity to inhibit weld lines. 